1. Field of the Invention
This invention relates to a spinneret for dry spinning spandex yarns. More particularly, the invention concerns an improvement in such a spinneret which results in dry-spun spandex yarns that are more uniform in linear density (i.e., denier or decitex).
2. Description of the Prior Art
The term "spandex", as used herein, has its usual definition, a long-chain synthetic polymer that comprises at least 85% by weight segmented polyurethane.
Dry-spinning of spandex polymer solutions through orifices to form filaments is known. For example, Smith, U.S. Pat. No. 3,094,374, and Hunt, U.S. Pat. No. 3,428,711, disclose such a process in which a spandex polymer is dissolved in a solvent to form a solution which is dry-spun through spinneret orifices in a spinning cell to form filaments. Upon emergence from the spinneret, the filaments are forwarded through a chamber of the cell, in which the solvent is evaporated from the filaments and the filaments are coalesced and adhered to each other to form a unitary thread. The thread is forwarded from the cell to a windup where it is formed into a yarn package.
Some spinnerets used commercially for producing coalesced spandex filaments of low decitex have two coaxial rings of grouped orifices. Such spinnerets are similar to those disclosed by Dreibelbis et al, U.S. Pat. No. 4,679,998. Usually, the number of grouped orifices in the outer ring is greater than the number in the inner ring. The number of individual orifices in each group of grouped orifices is usually three, four, five or six. Dreibelbis states that it is advantageous to space the orifices of each group of grouped orifices in the outer ring closer to each other than those of each group in the inner ring. This spacing was intended to decrease spandex thread power differences between the threads dry-spun from each group of orifices of the inner ring versus those from the outer ring. Usually, the coalesced thread from each orifice group is wound on a separate package. Thus many packages are formed from the threads issuing from one spinneret. In the past, to achieve higher throughput, attempts were made to increase the number of groups of filaments per spinneret, but such techniques often resulted in thread of inferior quality.
The known spinnerets generally have been satisfactory for preparing coalesced spandex filament yarns intended for various knit products. However, when such yarns were dry-spun at relatively low decitex and higher throughputs, their subsequent use in certain types of knitted hosiery too frequently produced "band"defects. Two-feed construction circular knit hosiery, such as that made with alternating courses of nylon and nylon-covered spandex yarns, appear to be especially susceptible to such band defects. The band defects usually were about two to five courses wide and covered a width of about 0.3 to 1 centimeter. One familiar with the art (e.g., Dreibelbis et al) would have suspected that the "band" defects were caused by differences between threadlines issuing from the inner and outer rings of grouped orifices. However, the problem was more complicated. Even when only one yarn was used to knit an entire piece of hosiery (e.g., a complete stocking), band defects were still present.
An object of the present invention is to provide means for producing dry-spun spandex threads that would greatly decrease band defects in circular-knit hosiery.
The present inventor found that band defects could be significantly decreased by dry-spinning the spandex threads with the spinneret of his invention. The use of the spinnerets of his invention rather than prior art commercial spinnerets resulted in less decitex variation along the length of each thread produced from each group of orifices and among threads produced from the inner versus outer rings of grouped orifices. This improvement apparently caused the band defects to be decreased substantially.